This is the main fortress inside the walls. It is a Norman structure. The guide said that the typical Norman structure was built in the shape of a cross. There was a central structure, and on each side of that was a tower which resulted in the shape of the cross. Trim Castle is one of the few Norman structures that was not modified since the 14th century. It is pretty much in its original form. The above picture is of the eastern side, which is the only side where the tower has fallen.
This is the draw bridge entrance from inside the outer walls.